The present invention is related to the inventors"" application Ser. No. 09/641,179 concurrently filed herewith and entitled xe2x80x9cBIDIRECTIONAL REPEATER USING HIGH AND LOW THRESHOLD DETECTIONxe2x80x9d the disclosures of which are hereby incorporated by reference.
The invention generally relates to voltage drivers, and more particularly to voltage stabilized low level drivers for a variety of applications.
Voltage drivers have been used for providing a voltage level to drive loads for various applications. Different applications require different types of voltage drivers. Many conventional voltage drivers are not stable. Some of them are temperature or Vcc dependent, while others are load current or load capacitance dependent. As a result, these conventional voltage drivers have their limitations in their applications. In a particular application relating an Inter Integrated Circuits (I2C) bus interfaces, unstable voltage drivers adversely affect the circuit performance.
Therefore, there is a need for a stable voltage driver that is independent of temperature, Vcc, load current and load capacitance.
The present invention provides a voltage stabilized low level driver that outputs a low level independent of temperature, Vcc, load current, and load capacitance.
According to one embodiment of the invention, a voltage driver having an output node is provided. The driver comprises a switching circuit and an operational amplifier. The switching circuit has a control terminal and an output terminal coupled to the output node. The amplifier has a first input terminal connected to the output node, a second input terminal connected to an input reference voltage, and an output terminal connected to the control terminal of the switching circuit. The amplifier is controlled by an external disable signal for switching on and off the amplifier. The amplifier, upon being switched on, drives the control terminal of the switching circuit to cause the output node to match the reference voltage. The amplifier, upon being switched off, drives the control terminal of the switching circuit to cause the output node to have a high impedance. The high impedance allows the output node to be pulled up by an external device to a predetermined level. In a specific embodiment, the switching circuit is a transistor, and the control terminal is a gate terminal of the transistor.
According to another embodiment of the invention, a voltage driver having an output node is provided. The driver comprises a switching circuit having a control terminal and an output terminal; an operational amplifier having a first input terminal, a second input terminal, and an output terminal that is connected to the control terminal of the switching circuit, the amplifier being controlled by an external disable signal for switching on and off the amplifier; an output protection circuit coupled between the output node and the output terminal of the switching circuit; a first input protection circuit coupled between the first input terminal of the amplifier and the output node; and a second input protection circuit coupled between the second input terminal of the amplifier and an input reference voltage. The amplifier, upon being switched on, drives the control terminal of the switching circuit to cause the output node to match the reference voltage. The amplifier, upon being switched off, drives the control terminal of the switching circuit to cause the output node to have a high impedance. The high impedance allows the output node to be pulled up by an external device to a predetermined level. In another embodiment, the driver further comprises a slew rate control circuit coupled between the output node and the control terminal of the switching circuit.
According to a third embodiment of the invention, a repeater incorporating a voltage driver of the invention is provided for use in an I2C bus interface.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.